1. Field of the Invention
The present invention provides a UV curable composition comprising an acrylate component, comprising an acrylate-functionalized hydrogenated polybutadiene, and at least one mono-functional acrylate, and a photoinitiator combination triggered upon exposure to radiation at 365 nm of the electromagnetic spectrum comprising a bisacyl phosphine oxide and benzophenone, where when dispensed at a thickness of about 1 mm and exposed to UV radiation generated at a wavelength of 365 nm the composition cures through the thickness of the dispensed composition at a speed between 40 mm/sec to 100 mm/sec.
2. Brief Description of Related Technology
Photocurable compositions are well known. Some may be based on acrylate functional groups, while others are based on vinyl ether or epoxy functional groups. These known photocurable compositions may include materials having oligomeric backbones, where the oligomer is a silicone based material, an acrylate base material, or a urethane base material.
In applications where microelectronic circuitry is to be coded with a curable composition, the material once coated desirably minimizes the ingress of environmental contaminants to that electronic circuitry. Should that not be the case, the environmental contaminants could cause corrosion in the circuitry, leading to electrical disconnect and failure of the electronic component. This clearly is highly undesirable.
While combinations of triphenyl phosphine oxide or bisacyl phosphine oxide with benzophenone have been described, benzophenone is used in these instances as a second photoinitiator. For instance, in International Patent Publication No. WO 02/22697 a methacrylate casting resin is described, in which among other things 0.1-10% phosphine oxide photoinitiator plus 0 to 10% of another photoinitiator, such as a benzophenone.
In addition, European Patent Publication No. EP 1 376 561 speaks to an adhesive composition targeted towards medical and electronics fields. The composition contains a urethane acrylate and an acrylamide, together with a photoinitiator component containing at least one acyl phosphine oxide and at least one additional photoinitiator, such as a benzophenone.
Notwithstanding the state of the art, as shown in the Examples, benzophenone is not a photoinitiator in the inventive composition, and does not itself produce radicals required to initiate polymerization upon exposure to UV light of a 365 nm wavelength, but rather requires an additional electron donor to do so.
Thus, it would be desirable to provide a photocurable composition having robust properties against the ingress of environmental contaminants, while curing at a fast cure profile.